In a device for measuring an acoustic wave, an acoustic-wave probe is used that receives a reflected wave (echo) generated by an acoustic wave irradiation to a target to be examined or a target site to be examined (hereinafter, simply referred to as a “target to be examined”) and outputs a signal. The device for measuring an acoustic wave displays electric signals converted from the reflected wave that is received by the acoustic-wave probe as an image. Thereby, an interior portion of the target to be examined can be visualized and observed.
As to the acoustic wave, a wave having a suitable frequency is selected among an ultrasonic wave, a photo acoustic wave, and the like, in accordance with a target to be examined, a measuring condition and the like.
For example, in an ultrasonic diagnosis device, by transmitting an ultrasonic wave toward an interior portion of the target to be examined and then receiving a ultrasonic wave reflected on a tissue inside the target to be examined, the interior portion is displayed as an image. In a device for measuring photo acoustic wave, by receiving an acoustic wave radiated from the interior portion of the target to be examined, due to a photo acoustic effect, the interior portion is displayed as an image. The photo acoustic effect means a phenomena in which when a pulse of electromagnetic waves such as a visible light, a far-red light, and a microwave is irradiated to the target to be examined, the target to be examined absorbs the electromagnetic waves and produces heat and thermally expands whereby an acoustic wave (typically an ultrasonic wave,) is generated.
A device for measuring an acoustic wave conducts transmission and reception of the acoustic wave with a living body which is a target to be examined, and therefore it has been desired to meet the requirements such as consistency of acoustic impedance with the living body and reduction of acoustic wave attenuation quantity.
For example, a probe for an ultrasonic diagnosis device being one of acoustic-wave probes (also referred to as an ultrasonic probe) is provided with a piezoelectric element transmitting and receiving an ultrasonic wave, and an acoustic lens which contacts with a living body. The ultrasonic wave transmitted from the piezoelectric element is entered to the living body through the acoustic lens. If a difference in acoustic impedance (density×sonic speed) between the acoustic lens and the living body is large, an ultrasonic wave is reflected on the surface of the living body, so that the ultrasonic wave is not efficiently entered into the living body, and therefore it is difficult to obtain a high resolution. Further, in order to transmit and receive an ultrasonic wave with high sensitivity, it is desired that ultrasonic attenuation quantity of the acoustic lens is small.
Therefore, as one of acoustic lens materials, a silicone resin is primarily used, which is close to the acoustic impedance (1.4 to 1.7×106 kg/m2/sec) of the living body and has a small ultrasonic attenuation quantity.
For example, Patent Literature 1 and the like propose a composition for an acoustic lens in which a silicone-based rubber (polyorganosiloxane), a butadiene-based rubber, or the like as a major ingredient is blended with an inorganic filler such as silica and the like.
Further, the acoustic lens is used in contact with the target to be examined, and therefore a mechanical strength enough to withstand long-term use thereof is required. For such occasions, Patent Literature 2 proposes a composition containing a powder of a silicone rubber, ytterbium oxide, or the like and silica particles, as a composition for an acoustic lens which satisfies acoustic lens characteristics (acoustic impedance, ultrasonic attenuation quantity, mechanical strength, and the like).